A spark plug for use in an internal combustion engine or the like includes, for example, an insulator having an axially extending axial hole; a center electrode inserted into a forward end portion of the axial hole; a tubular metallic shell provided around the insulator; and a rodlike ground electrode fixed to a forward end portion of the metallic shell. Also, a gap is formed between a distal end portion of the ground electrode and a forward end portion of the center electrode for generating spark discharge through application of voltage across the gap.
According to a known technique for improving resistance to spark-discharge-induced erosion, a tip formed of a metal having excellent durability, such as a noble metal alloy, is joined to a surface of the ground electrode which faces the forward end portion of the center electrode, thereby forming the gap between the tip and the forward end portion of the center electrode. Furthermore, in order to improve joining strength, at least a portion of the tip is embedded in the ground electrode along the thickness direction of the tip (refer to, for example, Patent Japanese Patent Application Laid-Open (kokai) No. 2012-94492).